Nanostructured materials having a nanoscale regular arrangement, such as multi-layer structure materials having a repeated structure of several to several tens of nanometers, are expected to have different properties from those of normal materials. Nanostructured materials having a multilayer structure are produced by, for example, a method in which layered crystals are exfoliated and deposited one layer by one layer by the layer-by-layer method (LBL method), a method in which thin films are deposited using a thin film forming technique such as sputtering, or other methods. However, since a multilayer structure is formed by sequentially depositing one layer by one layer in the LBL method or the method using a thin film forming technique, this brings about a problem that the procedure is complicated, especially when different kinds of material are used for every other layer. Moreover, some materials have a crystal structure which cannot be easily exfoliated and other materials cannot be formed into a film; accordingly, the kind of materials to which these methods are applicable is limited.
Further, US Patent Application Publication No. 2002/0187197 (PTL 1) discloses, in the specification, a method for producing a hollow polymer capsule having a multi layer structure. In the production method described in PTL 1, first, the surface of uncharged microcrystals is coated by self-assembly of charged surfactant molecules. Coating with the surfactant molecules makes continuous adsorption and deposition of polyelectrolytes possible. Each of the deposited polyelectrolyte layers has an opposite charge to that of a polyelectrolyte layer already adsorbed. Hence, electrolytes having charges opposite to each other are alternately deposited. Then, the coated uncharged microcrystals are removed by dissolution, and thereby a hollow polymer capsule having a multilayer structure is obtained. Nevertheless, the procedure of the method described in PTL 1 is also complicated because a multilayer structure is formed by sequentially depositing oppositely-charged polyelectrolyte layers one layer by one layer. In addition, although the hollow polymer capsule formed has a multilayer structure, deposition of the polyelectrolytes by adsorption results in a low degree of regularity.
Further, Japanese Unexamined Patent Application Publication No. 2003-327782 (PTL 2) discloses a method in which the surface of a substrate is coated with a composition containing a poly(methylphenylsilane) 3-methacryloxypropyltriethoxysilane (PMPS-co-PMPTES) block copolymer and Ti(OC2H5)4, and then heated for sol-gel reaction, followed by decomposition and removal of the polysilane segment to thus form an inorganic porous thin film on the substrate. Nevertheless, in the method described in PTL 2, although a hybrid of (PMPS-co-PMPTES)-titanium oxide is formed, a regularly-arranged structure like multilayer structure is not obtained. Moreover, the composition of a material to be obtained by this method is limited.
Moreover, Teranishi et al., “Conversion of Anisotropically Phase-Segregated Pd/γ-Fe2O3 Nanoparticles into Exchange-Coupled fct-FePd/α-Fe Nanocomposite Magnets”, J. Am. Chem. Soc., 2008, 130, 4210-4211 (NPL 1) discloses a method in which oleic acid, oleylamine, and Fe(acac)3 are dissolved in a Pd nanoparticles/1-octanol solution and then heated to synthesize Pd/γ-Fe2O3 nanoparticles having a γ-Fe2O3 phase anisotropically grown on the surface of the Pd nanoparticles, followed by calcination in a reducing gas atmosphere to obtain a FePd/α-Fe nanocomposite material. Nevertheless, in the method described in NPL 1, the particle diameter of the FePd nanoparticles dispersed in the Fe matrix and the distance among the particles greatly vary, and a structure having a periodic structure is not obtained.
Furthermore, Aizawa et al., “Nanoscale Patterning of Two Metals on Silicon Surfaces Using an ABC Triblock Copolymer Template” J. Am. Chem. Soc., 2006, 128, 5877-5886 (NPL 2) discloses a method in which a thin film of a block polymer is formed on a Si substrate, a raw material solution of Au and Ag is brought into contact with and impregnate the surface of the thin film, and then the block polymer is removed to obtain a AuAg nanostructure. Nevertheless, by the method described in NPL 2, a nanoscale pattern is formed with Au and Ag, but the pattern is two-dimensional, and a structure having a three-dimensional periodic structure is not obtained.
Moreover, Japanese Unexamined Patent Application Publication No. 2009-138014 (PTL 3) discloses a method for producing a nanostructured material, comprising: a raw material solution preparation step of preparing a raw material solution by dissolving, in a solvent, a block copolymer comprising a first polymer block component and a second polymer block component which are immiscible but linked to each other, and an inorganic precursor coordinated to the first polymer block component but not coordinated to the second polymer block component; and a nanostructure-forming step of forming a nanophase-separated structure in which a first polymer phase comprising the first polymer block component with the inorganic precursor coordinated thereto and a second polymer phase comprising the second polymer block component are regularly arranged by self-assembly. Further, PTL 3 states that it is possible to obtain a nanostructured material comprising the inorganic component by removing the block copolymer having such a nanophase-separated structure. It is also described that a second inorganic precursor coordinated to the second polymer block component may be dissolved in the solvent.